This invention relates to air compressors and more particularly to a dual stage, electric motor driven, portable air compressor which is unloaded at the suction side above a predetermined pressure level.
Portable air compressors have come into vogue recently because of the lack of services at many gasoline stations. Most of these compressors are designed to deliver air at pressures in the range of 0-100 psi and accordingly compromises are made among the size of the motor and compressor and quantity of air that can be delivered in a given amount of time. Most prior art compressors have piston displacement sized in relation to the available power of the electric motor so that the motor is operating at or somewhat over its rated power when pumping against the 100 psi outlet pressure. This causes the motor to run under very modest load when pumping in the normal tire pressure range of 25-30 psi. With such low piston displacement, delivery rates are low, resulting in long filling times.